Thae Yong Ho, who defected to South Korea in 2016, said in a news conference in Seoul on Tuesday that next week’s meeting in Vietnam will be a failure if Trump can’t get Kim to declare he will abandon all of his nuclear facilities and weapons and return North Korea to the nuclear non-proliferation agreement.

Thae worked as a minister at the North Korean Embassy in London before fleeing to South Korea. He is the highest-level North Korean diplomat to defect to the South.